The present invention relates to a screen for screening electrical and electronic circuits from the influence of any external magnetic and electrical fields. More particularly, the invention relates to screening circuits which are mounted for example on accounting machines, word processors, teleprinters, data terminals or other like machines.
In present machines of such type, to make them economical and light, the casings are normally of plastic material and the electrical circuits are usually disposed either between the mechanical parts of the machine and the bottom of the casing or between a side portion of the casing and the mechanical parts. Because the mechanical parts represent a considerable metal mass, they in turn in themselves provide good screening for the circuits, on the side on which the mechanical parts are disposed. To complete the screening for such circuits, a process is known which provides for internally coating the casing with a layer of metal which is produced for example by the known flame application process. The metal layer on the casing is then connected to the metal mechanical parts of the machine by means of conductors. When the mechanical parts are designed to be removable with respect to the casing, suitable connectors must be used to connect the two parts together.
This screening system, while guaranteeing good results, nonetheless suffers from the disadvantage of being too expensive.
The object of the present invention is to provide a screen for screening electrical circuits, which is simple, reliable and very economical. The screen according to the invention is characterised by a flexible sheet having an insulating layer towards the circuit to be screened, and a metal layer carried by the insulating layer.
A subsidiary object of the invention is to provide a screen wherein the parts of the screen can be easily connected to the mechanical parts of the machine, without the use of connectors.
Thus, the screen may be further characterised in that at least one portion of the flexible sheet is bent in such a way as to bring the corresponding metal layer into contact with the metal parts of the machine, and that a resilient element constantly urges this portion against the metal parts.